1. Field of the Invention
The present invention relates to a thermal head, a printer, and a method of manufacturing the thermal head.
2. Description of the Related Art
There are conventionally known a thermal printer to be mounted on a personal digital assistant as typified by a compact handy terminal, and a thermal head to be used in the thermal printer to perform printing on a thermal recording medium by selectively driving a plurality of heating elements based on print data. Longer battery duration is required for the personal digital assistant, and therefore a thermal head having high printing efficiency which reduces power consumption of a thermal printer is necessary.
The above-mentioned conventional thermal head includes an upper substrate, a support substrate which is bonded to the upper substrate on one surface side thereof in a laminated state and which is made of a glass material, a heat generating resistor provided on the upper substrate on the other surface side thereof, and an intermediate layer which is provided between the upper substrate and the support substrate and which has a cavity portion formed in a region opposing to the heat generating resistor. The conventional thermal head is designed to efficiently use heat generated in the heat generating resistor by high heat insulating performance of the cavity portion and the heat accumulation effect of the support substrate and to improve the heating efficiency.
However, the intermediate layer of this conventional thermal head is formed of a plate-shaped glass material having a melting point lower than those of the upper substrate and the support substrate. Therefore, a part of the cavity portion may be filled because of the reduced viscosity of the intermediate layer in melting, or the shape of the cavity portion may not be maintained and be crushed because of the load of the upper substrate. Therefore, there is a problem that a desired hollow shape is not obtained stably and a uniform and sufficient heat insulating effect is not exerted.